An aluminum-based metal material has conventionally been employed as die castings, heat exchangers, food containers, members for secondary battery, and the like. It has been known that the corrosion reaction of the aluminum-based metal material proceeds due to moisture and contaminants adhered to a surface thereof, leading to the generation of white rust. Therefore, a chemical conversion treatment is applied to the surface of the aluminum-based metal material for the purpose of providing with excellent white rust resistance (hereinafter referred to as “corrosion resistance”).
There have been proposed various chemical conversion agents capable of providing with excellent white rust resistance. A chemical conversion agent containing titanium complex fluoride ions, pentavalent vanadium compound ions, and zirconium complex fluoride ions are disclosed, for example, as a chemical conversion agent capable of providing a surface of aluminum or an alloy material thereof with satisfactory corrosion resistance (see Patent Document 1).
There is also disclosed, as technology capable of providing an aluminum-based metal material with excellent corrosion resistance, technology relating to a surface treatment agent including a resin compound having a specific structure, a vanadium compound, and a specific metal compound as essential components (see Patent Document 2). It is considered that this technology enables not only reduction of a vanadium compound but also significant improvement in stability of the vanadium compound, thus making it possible to maintain excellent corrosion resistance imparting effect for a long time by including a water-soluble organic compound having at least one functional group such as a hydroxyl group, a carbonyl group, or a carboxyl group, for example, ascorbic acid. It is also considered that the technology enables formation of a uniform coating film, thus making it possible to improve the level of corrosion resistance.
Regarding an aluminum-based metal material, an improvement in blackening resistance (hereinafter referred to as “moisture resistance”) has recently been regarded as important, in addition to an improvement in corrosion resistance. Herein, an indicator of corrosion resistance is white rust, whereas, an indicator of moisture resistance is blackening. White rust is a corrosion phenomenon generated by a corrosion factor such as oxygen, water, and chloride ions, whereas, blackening is a corrosion phenomenon generated by the existence of oxygen, water, and heat.
Meanwhile, a surface of an aluminum-based metal material is subjected to a lamination process for the purpose of providing with a design and protecting the surface. A laminate film used in the lamination process is excellent in processability, corrosion resistance, and barrier property of contents, and the like. Unlike paint, the laminate film is preferred in view of production environment since volatilization of an organic solvent does not occur. Such lamination process is often applied to a surface of a coil- or sheet-shaped aluminum-based metal material which is used in food containers and members for secondary battery.
The laminate film used in the lamination process has a problem that the laminate film might be peeled from a surface of the aluminum-based metal material when an advanced processing process is applied or a heat treatment is applied, since the laminate film has excellent properties mentioned above but is not sufficient in adhesion with a surface of an aluminum-based metal material. Such peeling of the laminate film may be a major factor which impairs appearance of the aluminum-based metal material, leading to deterioration of corrosion resistance of the aluminum-based metal material.
Thus, there is disclosed technology in which a metal surface treatment agent including a basic zirconium compound and/or a cerium compound, a carboxyl group-containing resin, and an oxazoline group-containing acrylic resin, and including no fluorine is applied to a surface of an aluminum-based metal material prior to a lamination process to form a surface treated layer, thus improving adhesion between a surface of a metal material and a laminate film (see Patent Document 3).
There is also disclosed technology in which a chemical conversion coating film is formed on a surface of an aluminum-based metal material using a chemical conversion agent including at least one polyvalent metal selected from the group consisting of zirconium, titanium, and chromium prior to a lamination process, and then a surface treated layer is formed using a metal surface treatment agent including an oxazoline group-containing resin and a primary amino group-containing resin (see Patent Document 4). It is considered that this technology enables an improvement in adhesion between a surface of a metal material and a laminate film, and also an improvement in corrosion resistance.
Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2010-261058
Patent Document 2: Japanese Unexamined Patent Application, Publication No. 2001-181860
Patent Document 3: Japanese Unexamined Patent Application, Publication No. 2009-84516
Patent Document 4: Japanese Unexamined Patent Application, Publication No. 2008-183523